1. Field of the Invention
The present invention relates to a wiring board in which conductive layers are formed on both surfaces of an insulating member, a multilayer wiring board in which an outer-layer wiring substrate is stacked onto at least one side of a wiring board, and a method for manufacturing these boards.
Priority is claimed from Japanese Patent Application No. 2005-110653, filed Apr. 7, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
FIG. 27 shows an example of a conventional multilayer wiring board. In the multilayer wiring board shown in this figure, outer-layer wiring substrates 110 are formed on both sides of the wiring board 100A.
In the wiring board 100A, conductive layers 102 are formed on both sides of the insulating member 101 having a penetrating hole (through-hole) 103. Openings are formed in the conductive layers 102 at positions corresponding to the penetrating hole 103. The conductive layers 102 are connected together by a conductive layer 105 formed on the surfaces of the conductive layers 102 and on the inner surface of the penetrating hole 103.
The outer-layer wiring substrates 110 comprise an insulating layer 107 in contact on one side with the conductive layer 105, and a conductive layer 106 formed on the other side of the insulating layer 107.
As shown in FIG. 28 and FIG. 29, in order to manufacture this multilayer wiring board, after using laser machining, drilling or the like to form the penetrating hole 103 in the insulating member 101, a plating method is used to form the conductive layer 105 on the surfaces of the conductive layers 102 and on the inner surface of the penetrating hole 103, followed by formation of the insulating layers 107 and conductive layers 106.
FIG. 30 shows another example of a conventional multilayer wiring board. The multilayer wiring board shown in FIG. 30 has outer-layer wiring substrates 110 formed on both surfaces of a wiring board 100B.
The wiring board 100B has conductive layers 102a and 102b formed on the both surface of the insulating member 101 which has an opening 104 (via). An opening is formed in the conductive layer 102a at a position corresponding to the opening 104. A conductive layer 108 is formed on the surface of the conductive layer 102a and on the inner surface of the opening 104. The conductive layer 108 formed on the conductive layer 102b within the opening 104 and thus the conductive layers 102a and 102b are connected.
As shown in FIG. 31 and FIG. 32, to manufacture this multilayer wiring board, after using laser machining or the like to form the opening 104 in the insulating member 101, a plating method is used to form the conductive layer 108 on the surface of the conductive layer 102a and on the inner surface of the opening 104, and then the insulating layer 107 and conductive layer 106 are formed.
However, because the penetrating hole 103 and opening 104 remain opened in this multilayer wiring board, there is the possibility that a recess may be generated in the conductive layer 106 in the portion corresponding to this penetrating hole 103 and opening 104. If a recess is generated in the conductive layer 106, it becomes difficult to mount an electronic component or the like in this portion, and the component mounting density is reduced, which is a disadvantage from the standpoint of reducing size and thickness.
In the wiring board 100B, the conductive layer 108 formed by a plating method is also formed on the surface of the conductive layer 102a in addition to the inner surface of the opening 104. Consequently, in the wiring board 100B, the conductive layer is thick, and formation of fine wiring patterns is difficult.
FIG. 33 shows an example of a wiring board which may be used in a multilayer wiring board. In this wiring board 100C, the conductive layer 109 is formed on the surface of the conductive layer 102a and in the opening 104, and the conductive layers 102a and 102b are connected by the conductive layer 109. The conductive layer 109 is formed so as to fill the opening 104, and accordingly the surface is flat.
When forming the conductive layer 109 by a plating method, the layer may be formed by continuing the supply of metallic material until the opening 104 is completely filled.
Because the surface of the conductive layer 109 is flat in a multilayer wiring board which uses this wiring board 100C, there is the advantage that recesses are not generated in the conductive layer of the outer-layer wiring substrate formed on the top.
However, in such a multilayer wiring board, the conductive layer 109 must be formed so as to fill the opening 104, and thus an increase in the thickness for the conductive layer 109 is unavoidable. As a result, formation of a fine pattern in the conductive layer 109 is difficult. Further, the conductive layer 109 is thick and the overall thickness is increased, which are disadvantageous for the reduction in the size and the thickness of the electrical/electronic apparatus.
Techniques relating to a variety of the above multilayer wiring boards are described in Kiyoshi Takagi, Birudoappu Tasou Purinto Haisenban Gijutsu, Nikkan Kogyo Shimbunsha.